108. Convert Sorted Array to Binary Search Tree

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def sortedArrayToBST(self, nums):
        """
        :type nums: List[int]
        :rtype: TreeNode
        """
        index=len(nums)
        if index==0:
            return None
        if index==1:
            return TreeNode(nums[0])
        
        cur=TreeNode(nums[index//2])
        cur.left =self.sortedArrayToBST(nums[:index//2])
        cur.right=self.sortedArrayToBST(nums[index//2+1:])
        return cur
        

class Solution:
    def sortedArrayToBST(self, nums):
        """
        :type nums: List[int]
        :rtype: TreeNode
        """
        return self.subSortedArrayToBST(nums,0,len(nums)-1)
        
    def subSortedArrayToBST(self,l,i,j):
        if l == [] :
            return []
        BST = TreeNode(l[(i+j+1)//2])
        if i <= (i+j+1)//2-1:
            BST.left = self.subSortedArrayToBST(l,i,(i+j+1)//2-1)
        if j >= (i+j+1)//2+1:
            BST.right = self.subSortedArrayToBST(l,(i+j+1)//2+1,j)
        return BST